def test_topological_sort_with_single_item():
graph = {1: set()}
assert [1] == topological_sort(graph)
def test_topological_sort_multiple_paths():
graph = {1: set([2, 3]), 2: set([3])}
assert [1, 2, 3] == topological_sort(graph)
def test_topological_sort_raises_on_loop():
graph = {1: set([2]), 2: set([3]), 3: set([1])}
with pytest.raises(ValueError):
topological_sort(graph)
def test_topological_sort_simple_chain():
graph = {1: set([2]), 2: set([3]), 3: set([4])}
assert [1, 2, 3, 4] == topological_sort(graph)
